Exegesis:

ho ‘that which’: i.e. ‘that condition,’ ‘that state of affairs,’ ‘that union (which God has effected).’

sunezeuxen (only here in Mark) ‘he yoked together’: both in classical Greek and in non-literary koiné Greek (cf. Moulton & Milligan) the word is used of the marital relationship.

anthrōpos mē chōrizetō ‘man is not to separate’: as Rawlinson points out ‘man’ here indicates not judicial authority, but the husband, for it was he who actually dissolved the marriage relationship by writing a certificate of divorce and giving it to his wife, without recourse to legal authorities.

chōrizō (only here in Mark) ‘divide,’ ‘separate’: Moulton & Milligan point out that the word was “almost … a technical term in connection with divorce.” Daube translates: “What therefore God hath married into one, let not man divorce.”

Translation:

Joined together, as in the case of joined in verse 7, must be treated with care to avoid vulgar connotations. In some instances the most satisfactory equivalent is ‘therefore, if God has made two people man and wife.’

Put asunder must not be taken in the purely literal sense of physical separation, a rendering which has likewise led to certain vulgar associations. The meaning here if often translatable as ‘cause to be divorced’ or ‘abandon.’ If the first clause is made conditional, the second may follow quite normally, e.g. ‘If God has made them man and wife, then no one should cause abandonment,’ referring here to the actual participants in the marriage, not to outside authorities.

Quoted with permission from Bratcher, Robert G. and Nida, Eugene A. A Handbook on the Gospel of Mark. (UBS Handbook Series). New York: UBS, 1961. For this and other handbooks for translators see here .